It was in the midst of the reign of Tiberius that, in a remote province of the Roman empire, the Saviour was crucified. Animated by an unparalleled missionary spirit, His followers traversed the length and breadth of the empire, preaching everywhere the "glad tidings." Men's loss of faith in the gods of the old mythologies, the softening and liberalizing influence of Greek culture, the unification of the whole civilized world under a single government, the widespread suffering and the inexpressible weariness of the oppressed and servile classes,--all these things had prepared the soil for the seed of the new doctrines. In less than three centuries the Pagan empire had become Christian not only in name, but also very largely in fact. This conversion of Rome is one of the most important events in all history. A new element is here introduced into civilization, an element which we shall find giving color and character to very much of the story of the eighteen centuries that we have yet to study. REIGN OF CALIGULA (A.D. 37-41).--Caius Cæsar, better known as Caligula, was only twenty-five years of age when the death of Tiberius called him to the throne. His career was very similar to that of Tiberius. After a few months spent in arduous application to the affairs of the empire, during which time his many acts of kindness and piety won for him the affections of all classes, the mind of the young emperor became unsettled, and he began to indulge in all sorts of insanities. The cruel sports of the amphitheatre possessed for him a strange fascination. When animals failed, he ordered spectators to be seized indiscriminately, and thrown to the beasts. He entered the lists himself, and fought as a gladiator upon the arena. In a sanguinary mood, he wished that "the people of Rome had but one neck." As an insult to his nobles, he gave out that he proposed to make his favorite horse, Incitatus, consul. He declared himself divine, and removing the heads of Jupiter's statues, put on his own. After four years the insane career of Caligula was brought to a close by some of the officers of the prætorian guard, whom he had wantonly insulted. REIGN OF CLAUDIUS (A.D. 4l-54).--The reign of Claudius, Caligula's successor, was signalized by the conquest of Britain. Nearly a century had now passed since the invasion of the island by Julius Cæsar, who, as has been seen (see p. 292), simply made a reconnoissance of the island and then withdrew. Claudius conquered all the southern portion of the island, and founded many colonies, which in time became important centres of Roman trade and culture. The leader of the Britons was Caractacus. He was taken captive and carried to Rome. Gazing in astonishment upon the magnificence of the imperial city, he exclaimed, "How can a people possessed of such splendor at home envy Caractacus his humble cottage in Britain?"